Booster units have been used to improve the performance and coverage of known cellular radio-telephone systems. One type of booster is disclosed in Leslie et al. U.S. Pat. No. 4,941,200 entitled "Booster", assigned to the assignee of the present invention and incorporated herein by reference.
Boosters of the type disclosed in the above-noted Leslie et al. patent translate the boosted output to a frequency that is different from the received frequency The cell site that is nominally controlling the mobile or movable transceiver is unaware of this frequency change.
Previous boosters could hand-in from several cell-sites but were limited to handing back to the same cell-site. Therefore, in the small number of instances when a boosted call continued long enough for the mobile to drive out of the booster's and the donor's range, the call would drop.
The "hand-back to a different cell-site" dilemma occurs simply because to the serving cellular system the mobile is on one voice channel while the booster actually has it translated to another. When a boosted mobile drives out of the booster's range, the signal will become weak at the booster and the donor (the reverse path is linear).
The donor cell will then identify the mobile as a candidate for hand-off and the cellular system will try to find the mobile in the cell-sites adjacent to the donor cell site. Since the mobile is actually on the booster's translated voice channel, it will not be detected and located and hand-off will not occur.
Thus, it would be desirable to be able to provide an apparatus usable by the adjacent cell-sites to detect the mobile on the voice channel assigned by the donor cell. Once this has been accomplished, the cellular system can determine which adjacent cell the mobile is driving into, assign a voice channel in that cell, and then send a hand-off message for the mobile to go to that channel.